This paper has applied the mathematical process of reconstruction of a three dimensional objects as used in Computer Axial Tomography (ChT). It uses direct convolution techniques with functions defined in the real space of the object either with parallel projections or with fan-beam pro jections. The simulated data is obtained using a disk having a uniform density from the centre up to radius equal 0.8 except for an off centre numplbeyond which it tends smoothly to zero if the radius equals1.2. The data has been simulated at different sample intervals and different projection angles. The reconstructed image by using the convolution techniques with two types of filters for parallel ray and fan-beam has acceptable error that does not exceed 2$ at greater number of projections and smaller sampling interval .